The present invention pertains to the composite structure manufacturing art and, more particularly, to a method of, and apparatus for, forming and delivering a multifilament band to a receiving surface.
Composite material technology provides a means to fabricate a high-strength, low-weight structure. Such technology finds particular application in the aerospace industry.
At present, three principal composite manufacturing methods are practiced. These include tape lay-up, cloth or woven broad good lay-up, and filament winding. Each of these manufacturing techniques exhibits serious limitations, as is discussed below.
Tape lay-up composite material manufacturing is comprised of the laying of sections of tape side-by-side, or in an overlapped relationship, to form the composite structure. This lay-up may be accomplished manually, with mechanical assist, or by fully automatic tape lay-up machines. The fabrication of complex shapes, such as corners, bevels and tapered sections, is a tedious process using the tape lay-up method. Often, successive tape sections must be of different widths and/or lengths. A certain amount of overlap often occurs, which is undesirable.
In addition, where the tape is required to form a compound-curved surface, undesirable tape buckling occurs on the edge having the smallest radius of curvature. Further, where changes in direction are required, the tape must be cut and spliced to avoid buckling.
In addition, ply thickness is fixed for a given tape. If changes in either ply thickness or tape width are required, the process must be interrupted to change tape spools.
Close tolerance cloth broad good lamination is difficult to mechanize or automate. Further, cutting out contours and laminating these contour shapes is a cost-intensive procedure and often realizes significant material trim losses. In addition, design compromises must be made due to the inability to select any desired fiber angle and the requirement to shingle layer to obtain tapers.
To make optimum use of the potential of composite materials, the filament should be consistently and accurately aligned in the direction of the loads being carried, with the quantities of filaments being consistently matched to the load requirements. This requirement can be met relatively easily when the structure and load pattern are geometrically simple.
Industry-wide, a limited amount of work has been accomplished in the development of a preimpregnated graphite fiber delivery system specifically for filament winding aircraft quality structures. Standard filament winding practices seldom require the manufacturing quality control required for aircraft structural parts. Resin content control, fiber bandwidth control, and bandwidth thickness must all be addressed for filament winding to be useful in aircraft composite structures.
In most cases, the filament winding methods presently used in industry to wind with preimpregnated fibers employ standard winding high-technology in combination with fiberglass or Kevlar preimpregnated rovings. Graphite rovings present specific problems due to their limited strength in shear when compared to Kevlar or fiberglass. Standard industry practice is to pull a roving through a winding eye. If a graphite preimpregnated roving is pulled over such a typical winding eye surface in an attempt to form a fiber band, resin tack-induced friction begins to cause the roving's outer fiber strands to be degraded, fuzz, or fail to shear. In a short period of time, considerable fiber fuzz and resin build-up occurs on the winding eye surface. The problem is compounded in the fiber delivery rate increases.